World Aquaculture December 2020

WWW.WA S.ORG • WORLD AQUACULTURE • DECEMBER 2020 63 evaluation tool of fish development based on slight modifications in bilateral characteristics (Clarke 1992, Rasmuson 2002). Morphometric measurements were made on more than 50 fish per strain. Eye diameter, pectoral fin, upper lateral line, lower lateral line, pelvic spine, length between the nostril and the pelvic spine insertion and the length of nostril to the insertion of the pectoral fin were measured. There was an increase of FA in the GenoMar strain, specifically in gill raker and opercular lengths. There was no difference between the FA of GIFT and FaST strains. The GenoMar strain may have experienced high levels of environmental stress or genetic deterioration. The growth response of GIFT, FaST, and domesticated tilapia strains was different (Romana-Eguia et al . 2010). The growth of GIFT strains (1.36 percent/d) was greater than that of the FaST strain (1.31 percent/d) and domesticated tilapia strains (1.26 percent/d). Differences in growth rate were attributed to genetic factors under controlled culture conditions (i.e. tank culture systems). On the other hand, environmental factors affected fish survival and growth response under uncontrolled culture conditions, lake-based cages. The daily growth rate, mean weight, feed conversion ratio and survival of GIFT and FaST strains and non-improved Nile tilapia were compared (Ridha 2006). The GIFT and FaST strains had greater mean weight, growth rate, survival, production and lower feed conversion ratio, affirming that these two strains are superior to non- improved Nile tilapia (Ridha 2006). SaltUno Tilapia Strain SaltUno tilapia, also known as Molobicus tilapia, is a strain produced by hybridization between Nile tilapia and Mozambique tilapia (Romana-Eguia et al . 2019). Mozambique tilapia can survive and grow at a salinity of 69 ppt and can spawn at a salinity of 49 ppt (Eguia and Romana-Eguia 2016). Nonetheless, it cannot grow as fast as the Nile tilapia, which is mainly grown in freshwater. A project between France’s Center for International Cooperation for Research and Development in Agricultural Science and the Philippine Council for Aquatic and Marine Research and Development of the Department of Science and Technology initiated the development of the Molobicus tilapia (Guerrero 2018). They found no differences between the growth of hybrid Molobicus tilapia and Nile tilapia. Moreover, the hybrid was more salt tolerant than Nile tilapia. BEST strain The BEST strain, developed by BFAR, can withstand a certain level of salinity, making polyculture in brackishwater systems feasible. It was developed via hybridization and outcrossing different tilapia strains that were selected based on a specific size for saline tolerance (Romana-Eguia et al. 2019). Four purebreeds and crossbreeds of Oreochromis spp. were used for development of the BEST strain: O. niloticus , O. spilurus , O. aureus and O. mossambicus (Tayamen et al . 2002). Two female tilapias were exposed to one male in a hapa. The premaxilla of each male was clipped to avoid female mortality as males have a tendency to be aggressive toward females. Males were transferred to another hapa after the females spawned. Fingerlings were placed in ten environments with salinity ranging from 0 to 42 ppt. Body weight was greatest in progenies of O. aureus × O. spilurus . Survival was high in low-salinity waters (0-12 ppt). Although survival rates were low, tilapia tolerated and survived salinities of 15-32 ppt. Growth performance of the BEST strain in organically fertilized brackishwater ponds at three different stocking densities has been assessed (Labastida et al. 2015). The greatest average body weight was observed in strains cultured in a semi-extensive system (223 g), better than those cultured in intensive (215 g) and extensive (52 g) systems. However, the best survival rate was found in strains cultured in an extensive system (92 percent) but survival was also good in a semi-extensive (80 percent) and intensive (84 percent) systems. Economic return analysis showed that BEST strain cultured in an intensive system provided a return of investment of 139 percent with a 0.71-yr payback period. GET-EXCEL strain The GET-EXCEL strain was developed for better growth and survival rate by crossbreeding the fast-growing GIFT, FAST, Egypt and Kenya strains using within-family selection and mating rotation (Tayamen 2004, Romana-Eguia et al. 2019). The GET-EXCEL strain was developed to compete with global standards and increase local production. Rural farms suffered from decreased tilapia production due to insufficient supply of fish fry and degraded quality linked to inbreeding. GET-EXCEL tilapia had a 38-g growth advantage and 10 percent increase in survival rate compared with commercial tilapia. It was also resistant to common stressors such as temperature fluctuations and diseases (dela Cruz 2003) and had good-quality These 2-3 cm tilapia fry have been sex-reversed with androgenic hormones to produce monosex males, thereby promoting faster growth. These fry are sold for US$ 0.10 each (Photo: T.O. Magbanua). ( C O N T I N U E D O N P A G E 6 4 )